1. Field of the Invention
The present invention relates to a microbial hydrogen-producing process having high efficiency, high stability, and high reproducibility, which co-culturing at least one Clostridium microbe and at least one Bacillus microbe in a fermentation culture system to produce hydrogen.
2. Description of the Related Art
In recent years, the excessive consumption of fossil fuel has caused energy shortage and global climate change; therefore, more and more attentions are attracted to the alternative energy resources, in which hydrogen and ethanol are focused. To solve this problem, some researchers have suggested using renewable biomass resources as energy resources, thus and so, the problems caused by organic waste can also be solved (Lay 2000; Lay 2001). Since then, the bio-energy production from wastewater or solid waste by microbial fermentation has been considered as an environmentally friendly energy-producing process.
Hydrogen can be produced by water electrolysis, but the electricity cost is high. Although solar-powered water electrolysis equipments are used to produce hydrogen, it is not able to be popularized because the solar energy supply is unstable and the equipments are expensive. Thus, the microbial hydrogen production has been studied from 1970s. Hydrogen-producing microbes are generally comprised in anaerobes, facultative anaerobes, aerobes and photosynthetic bacteria comprise. In these microbes, hydrogenase is involved in many metabolic processes, which not only oxidizes hydrogen gas to hydrogen ions and electrons, but also reduces hydrogen ions and electrons to hydrogen gas (H2⇄2H++2e−); however, its regulation mechanism is still needed to be further studied.
The traditional hydrogen-producing fermentation chamber is a complicated open system composed of a variety of bacteria and the operation of this system is not stable. In addition, the conventional screening method cannot effectively identify the hydrogen-producing microbes, because the bacteria predominant in number may not the bacteria having hydrogen-producing capacity, and it is difficult to estimate the hydrogen-producing contribution of each screened bacterium. In addition, microbes from the same genus but different species may have different hydrogen-producing capacity, even microbes from the same species may have completely different hydrogen-producing capacity because they are obtained from different sources and belong to different strains. This is a great difficulty with which the microbial hydrogen-producing researchers have faced.
It has been known that the acetone-butanol-ethanol fermentation (ABE fermentation) of Clostridium microbes transfers carbohydrates to acetone, butanol and ethanol, and produces hydrogen at the same time. Clostridium beijerinckii, which is utilized in the current studies, has an exceptional ABE fermentation performance (Shaheen et al., 2000). Clostridium beijerinckii can decompose carbohydrates released from a variety of plants (Ezeji et al., 2007), but it is not economical because hydrolysis must be performed before fermentation. On the other hand, Bacillus microbes have been applied to the environmental sanitation industry to decompose complicated insoluble substances to soluble monomers for a long time (Clerek et al., 2004). Specifically, Bacillus thermoamylovorans is an important microbe in the compost, and it can transfer sludge and food waste into an organic fertilizer (Ivanov et al., 2004; Wang et al., 2003). However, no study shows the way how to apply these bacteria to hydrogen production of organic wastes, and how to develop an energy system for clean energy production and resources regeneration.